Hissin nailed it....I got a a replacement for $10 at Discount Auto....They are steel instead of AL, which means you can tq the bolts down tight....they also have an extra hole in the top to thread in an aftermarket sensor. While youre at it, grab a t-stat for an extra $8 and throw it in there.
Not all the aftermarket ones are steel, so be careful -- a buddy of mine broke his aluminum one torquing it down, and we went down to NAPA and picked up a new one. It was cast iron, not steel, and brittle. Guess what happened .